Production of substituted nitrophenols



United States PRODUCTION OF SUBSTITUTED NITROPHENOLS No Drawing. Filed Sept. 8, 1954, Ser. No. 454,818 Claims priority, application Germany Sept. 9, 1953 8 Claims. (Cl. 260-622) This invention relates to a process for the production of substituted nitrophenols.

It is well known that in the nitration of phenol a mixture of p-nitrophenol and o-nitrophenol is obtained. In contrast thereto, certain esters of phenol, as for example the esters of phenol with benzene sulfonic acid, and p-toluene sulfonic acid and aand B-naphthalene sulfonic acid, yield almost exclusively the corresponding p-nitrophenol ester which may be saponified to produce p-nitrophenol.

In the nitration of esters of substituted phenols the pand m-position, respectively, are much less fa'vored, substantial amounts of the corresponding o-nitrophenol ester being formed.

It is an object of the present invention to provide a process for the production of substituted mand p-nitrophenols. Another object is to provide a process for the production of substituted nitrophenols in which only a small amount of the o-nitro derivative is formed. A further object is to provide a process for the production of 4-nitro-3-chlorop-henol. Still further objects will become apparent hereinafter.

Very surprisingly, it has now been found that in the nitration of esters of substituted phenols the phosphoric acid esters basically dilfer from the other esters. While the esters of substituted phenols with carbonic acid, acetic acid, benzene sulfonic acid, etc. yield considerable amounts of the corresponding o-nitro derivative in addition to the mor p-nitro derivative, the phosphoric acid esters of substituted phenols form only small amounts of the corresponding o-nitro derivative, the main product being the mor the p-nitro compound.

Thus, in accordance with the present invention there is provided a process for the production of substituted nitrophenols which comprises converting a substituted phenol into its phosphoric acid ester, nitrating said phosphoric acid ester and saponifying the nitro esters thus obtained to form a substituted mor p-nitrophenol.

The following experimental rmults are given to illustrate the invention:

By nitration of o-cresyl phosphate and subsequent saponification there are obtained 99% of 4-nitro-2-methylphenol and only 1% of 6-nitro-2-methyl phenol.

The results obtained in the nitration of various esters of m-chlorophenol are shown in the following table:

As may be seen from the table, in the case of the atnt 0* 2,985,688 Patented May 23, 1961 ice phosphoric ester the smallest amount of the onitro derivative (6-nitro-3-chlorophenol) is formed while the p-nitro compound (4-nitro-3-chlorophenol) is produced in a maximum yield.

By nitration of m-cresyl phosphate and subsequent saponification there are obtained 1.5% of 6-nitro-3- methyl phenol and 98.5% of 4-nitro-3-methyl phenol.

The nitration of phosphoric acid esters of phenols carrying an ortho-para-directing substituent in the p-position results largely in the formation of the corresponding m-nitro compound, while the o-nitro derivative is obtained only in a small amount. Thus, by nitrating p-chlorophenyl phosphate and saponifying the nitration product there are obtained 70.5% of 3-nitro-4-chlorophenol and 29.5% of 2-nitm-4-chlorophenol. From p-cresyl phosphate there are obtained 97% of 3-nitro-4-methyl phenol and 3% of 2-nitro-4-methyl phenol.

The nitration of phosphoric acid esters of phenols carrying ortho-para-directing substituents in the oand p-position, as for example 2,4-dichlorophenol, 4-chloro- Z-methyl phenol and 4-methyl-2-chlorophenol, gives rise almost exclusively to the formation of the corresponding m-nitro compound, the o'-nitro derivative being produced only in a negligible amount.

The phosphoric acid esters serving as the starting material for the process of the invention may easily be obtained by reacting 3 mols of the substituted phenol with 1 mol of phosphoryl chloride. An attractive feature of the phosphoric acid esters is that they are more soluble in the conventional nitrating mixtures than the esters of the substituted phenols with other acids.

The method of the present invention will be apparent to those skilled in the art from a consideration of the following examples, which are illustrative only and are in no way to be construed as limiting:

Example 1 143.2 grams /a mol) tris-(pchlorophenyl)-pl1osphate (M.P. 112 C.) are dissolved at 0-10 C. in 400 cc. of sulfuric acid. While cooling and stirring, 190 grams of a mixture consisting of 33% of nitric acid and 67% of sulfuric acid are then added dropwise at such a rate as to maintain the temperature between 5 and +10 C. Upon stirring the reaction mixture 4 hours at 20 C. it is poured into 1 liter of water. The aqueous mixture thus obtained is steam distilled until all the 2-nitro-4-chlorophenol formed has passed over. From the distillate there are recovered 50.7 grams (29.2%) of 2-nitro-4-chlorophenol melting at 87 C. The residue from the steam distillation is cooled, whereby crude 3-nitro-4-chlorophenol is crystallized. The product is filtered off by suction, washed with water and dried. Yield of 3-nitro-4-chlorophenol: 122 grams (70.3%). M.P. (upon recrystallization from benzene): 126.5 C.

Example 2 143.2 grams /3 mol) of tris-(m-chlorophenyl)-phosphate (B.P. 230 C./0.04n1m.) are dissolved in 180 cc. of 96% sulfuric acid at a temperature below 10 C. To the solution there are added drop'wise at 5 l0 C. 1.90 grams of -a mixture consisting of 33% of nitric acid and 67% of sulfuric acid while cooling and stirring. Upon stirring for 3 hours at 20 C. the mixture is poured into 500 cc. of water and then steam distilled. 19.9 grams (11.5%) of 6-nitro-3-chlorophenol, M.P. 41.5 C., go over along with 3 liters of Water.

From the residue of the steam distillation 4-nitro-3- chlorophenol crystallizes upon cooling. The product is filtered off by suction, Washed with water and dried. Yield: 150.5 grams (86.8%). Upon recrystallization from benzene there are obtained 131.5 grams (75.8%) of 4-nitro-3-chlorophenol melting at 124.5 C.

3 Example 3 471.5 grams (1 mol) of tris-(2-chloro-4-methyl phenyl)-phosphate (M.P. 106 C.) are dissolved at a temperature below 15 C. in 1,500 cc. of 100% sulfuric acid and nitrated at -10 C. with 570 grams of a mixture consisting of 33% of nitric acid and 67% of sulfuric acid. Upon stirring for 6 hours at 20 C. the reaction mixture is poured into 2 liters of water. The resulting mixture is refluxed for 4 hours. On cooling 2-chloro-4-methyl-5-nitrophenol crystallizes. The crystals are filtered off with suction, washed with water and dried. Yield: 580 grams (97.7%). MP. 96-98 C. The product may be purified by sublimation or via its poorly soluble ammonium salt. Melting point upon purification: 101.5 C.

The isomeric 2-chloro-4-rnethyl-6-nitropheno1 is not formed in an appreciable amount.

While the above description points out the preferred embodiments of our invention, it is to be understood that departures may be made therefrom within the scope of the invention as described and claimed.

We claim:

1. Process for the production of substituted nitrophenols, which comprises converting a phenol selected from the group consisting of mono-substituted phenols substituted in one of the mand p-positions and disubstituted phenols substituted in one of the o-positions and the p-position with substituents selected from the group consisting of chlorine and methyl groups into its phosphoric acid ester, nitrating said phosphoric acid ester in the presence of at least 96% sulfuric acid and sap onifying the nitration product to form a substituted nitrophenol containing a substantial quantity of the substituted m-nitrophenol free from a substantial quantity of the substituted o-nitrophenol.

2. Process in accordance with claim 1, in which said phosphoric acid ester is obtained by reacting a substituted phenol with phosphoryl chloride.

3. Process in accordance with claim 1, in which said saponification is carried out by heating the nitration product with Water.

4. Process for the production of 3-nitro-4-chlorophenol, which comprises converting p-chlorophenol into tris-(p-chlorophenyl)-phosphate, nitrating tris-(p-chlorophenyl) -phosphate, saponifying the nitration product and recovering 3-nitro-4-chlorophenol.

5. Process for the production of 4-nitro-3-chlorophenol, which comprises converting m-chlorophenol into tris-(m-chlorophenyl)-phosphate, nitrating tris-(m-chlorophenyl) phosphate, saponifying the nitration product and recovering 4-nitro-3-chlorophenol.

6. Process for the production of 2-chloro-4-methyl- S-nitrophenol, which comprises converting 2-chloro4- methyl phenol into tris-(2-ch10ro-4-methyl phenyl)-phosphate, nitrating tns-(2-chloro-4-methyl phenyD-phosphate, saponifying the nitration product and recovering 2-chloro- 4-methyl-5-nitrophenol.

7. Process for the production of substituted nitrophenols which comprises nitrating a phosphoric acid ester of a phenol selected from the group consisting of monosubstituted phenols substituted in one of the m-, 0-, and p-positions and di-substituted phenols substituted in two of the m-, oand p-positions with substituents selected from the group consisting of chlorine and methyl groups in the presence of at least 96% sulfuric acid, and saponifying the nitration product to form a substituted nitrophenol containing a substantial quantity of the substituted m-nitrophenol free from a substantial quantity of the substituted o-nitrophenol.

8. Process for the production of 4-nitro-3-chlorophenol which comprises nitrating tris-(m-chlorophenyl)-phosphate, saponifying the nitration product and recovering the 4-nitro-3-chlorophenol formed.

References Cited in the file of this patent Rapp: Annalen der Chemie, vol. 224 (1884), pp. 172-178 (7 pages), entire article pp. 156-178.

Hoeflake: Chem. Abstracts, vol. 11 (1917), pp. 42-45 (4 pages).

Ketelaar et al.: Rec. Trav. Chim., vol. 71 (1952), pp. 1253-8 (6 pages). 

1. PROCESS FOR THE PRODUCTION OF SUBSTITUTED NITROPHENOLS, WHICH COMPRISES CONVERTING A PHENOL SELECTED FROM THE GROUP CONSISTING OF MONO-SUBSTITUTED PHENOLS SUBSTITUTED IN ONE OF THE M- AND P-POSITIONS AND DISUBSTITUTED PHENOLS SUBSTITUTED IN ONE OF THE O-POSITIONS AND THE P-POSITION WITH SUBSTITUENTS SELECTED FROM THE GROUP CONSISTING OF CHLORINE AND METHYL GROUPS INTO ITS PHOSPHORIC ACID ESTER, NITRATING SAID PHOSPHERIC ACID ESTER IN THE PRESENCE OF AT LEAST 96% SULFURIC ACID AND SAPONIFYING THE NITRATION PRODUCT TO FORM A SUBSTITUTED NITROPHENOL CONTAINING A SUBSTANTIAL QUANTITY OF THE SUBSTITUTED M-NITROPHENOL FREE FROM A SUBSTANTIAL QUANTITY OF THE SUBSTITUTED O-NITROPHENOL. 